Factbox: Parties and politics in Iran's parliamentary election

Political infighting has intensified among Iran's faction-ridden elite since a nuclear deal was reached with six major powers last year that led to lifting of crippling sanctions in return for curbing Tehran's nuclear program.

The country's top authority, Supreme Leader Ayatollah Ali Khamenei, and Rouhani have called for a high turnout after half of the candidates, mostly moderates, were disqualified by a hardline watchdog body, the Guardian Council.

Leading pro-reform parties and politicians have criticized the disqualifications, but say that they have no intention of boycotting the vote.

The current parliament is dominated by Rouhani's hardline rivals, who reject his economic policy of boosting foreign trade and investment.

Following are some facts about Iran's 10th parliamentary election since the 1979 Islamic Revolution.

* CANDIDATE VETTING

- Candidates for the 290-seat assembly were screened by government-run committees and the Guardian Council, a hardline body of six clerics and six law experts that checks hopefuls for commitment to Islam, their belief in the Velayat-e Faqih (religious system of law) and the pillars of Iran's revolution.

- After the vetting process, some 6,300 candidates were allowed to enter the race out of an unprecedented number of more than 12,000 potential hopefuls who registered to run for the elections of parliament and the Assembly of Experts, which has the authority to appoint or dismiss the supreme leader.

* MAJOR POLITICAL FACTIONS

- Iran has over 250 registered political parties, according to the Interior Ministry. But it has no tradition of disciplined party membership or detailed party platforms. Two main pro-reform parties were banned after the 2009 election that led to hardline President Mahmoud Ahmadinejad's second-term win. Months of anti-government protests followed.

In major cities like Tehran, two main groups have emerged but some candidates are backed by more than one group and allegiances often shift.

- The United Front of Principlists: The biggest hardline group, encompassing loyalists to Khamenei, emphasizing Islamic social values and support a free market economy. This group is supported by the establishment's backbone - influential clerics, the elite Revolutionary Guards and powerful bazaar merchants.

The coalition includes various parties like the Devotees and Path-seekers of the Islamic Revolution, the Front of Islamic Revolution Stability, Islamic Coalition Party and the Association of Combatant Clergy.

They are trying to agree on a united lists for major cities, like Tehran with 30 seats. But they still remain split.

- Some pragmatic principlists, most notably parliament speaker Ali Larijani, fall in the middle of Iran's political spectrum, working with both principlists and pro-reform parties.

- The Pro-Reform Front: The alliance is made up of members of dozens of parties, including the Union of Islamic Iran People Party, Nedaye Iranian, Iranian-Islamic Freedom Party, Association of Combatant Clerics, Islamic Labor Party and Moderation and Development Party.

As most of prominent pro-reform candidates have been disqualified, the main pro-reform parties have agreed on a joint list of candidates, the “Alliance of Reformists and Government Supporters”, which will include women and young candidates.

- Independent candidates in small cities and towns could attract more support as the vote in such places would depend on the reputation of candidates and personal contacts with voters.

* THE VOTE AND THE RESULT

- There are about 50 million eligible voters, who must be over 18 years, in the country of around 80 million people.

- All ballots will be counted manually so the final result may not be announced for three days, although partial results may appear sooner.

- Iran’s constitution mandates five reserved seats in parliament for religious minorities.

* CAMPAIGNING

- The parliamentary election campaign will be from Feb. 18-24.

* A NEW PARLIAMENT

- Iran's parliament does not determine policy in areas such as Iran's foreign affairs, but it plays a major role in economic policy and winning a majority is critical for factions that jockey for position before the 2017 presidential race.

The pro-reform alliance is seeking a greater share of the parliament, where hardliners have dominated for more than a decade.

(Writing by Parisa Hafezi; Editing by Dominic Evans)